1. Field of the Invention
The invention relates in general to an optical disk drive, and more particularly to a method and a device for quickly reading data by controlling an optical head to move in different ways when the optical disk drive is reading data on an optical disk.
2. Description of the Related Art
The conventional optical disk has concentric circles or a spiral track. The track is divided into several data blocks each having an address and for recording data. When the data on the optical disk is being read, the track has to be locked and sought. The required data cannot be correctly read until the address of the data block is reached.
FIG. 1 (Prior Art) is a flow chart showing a reading method for a conventional optical disk drive in Taiwan Patent No. 1238386. In step P1, the conventional optical disk receives a command of an external host for reading data on the optical disk, and the operation of reading the data is started. Next, in step P2, it is checked whether cache data in a memory contains the required data to be read according to the command. If the cache data contains the required data, the procedure enters step P3, and the required data is directly read from the memory and replied to the host in step P8. If the cache data does not contain the required data, the procedure enters step P4, in which the block address of the required data is obtained according to the catalogue information of the optical disk, and the position of the optical disk where the required data may be read is set.
Next, in step P5, the optical head is moved across the track from the current position to the set position. Then, the procedure enters step P6 to lock the track and seek the track and read the data to the memory. In step P7, the read data in the memory is processed and interpreted into the required data stored in the memory to serve as the cache data. Then, in step P8, the interpreted required data is replied to the host. At last, the command of the host of reading the data ends in step P9. Therefore, the optical disk drive may utilize the data pre-stored in the memory as the cache data to increase the speed of the optical disk drive for reading the data.
However, when the memory of the conventional optical disk drive does not contain the cache data to be read by the host, the optical head has to jump to the block address of the required data of the optical disk to read the data. The track jumping servo has to calculate the number of tracks and the distance of track jumping, to ensure that the objective lens is within the range where the optical head can maintain the signal, to unlock the track to form the servo open-loop, and then to apply a suitable driving force to the optical head so that the optical head can jump to the target track, and then form the servo closed-loop, lock the read track and determine whether the optical head reaches the target track or not. If not, the track jumping operation is performed again until the optical head reaches the target track so that the required data can be correctly read.
The optical disk is rotated at a very high speed relative to the optical head, and the tracks are very dense or even the track may have the eccentric deformation. So, the typical track jumping needs to be performed many times so that the optical head can reach the target track. Thus, it is very time-consuming. More particularly, in order to finish the reading command, many times of track jumping have to be continuously performed in the optical disk drive to read the discontinuous required data from many positions and the operations become more time-consuming. In addition, the capacity of the memory of the optical disk drive is limited, and the memory mainly serves as the buffer memory for processing the data and cannot save a lot of cache data. The optical disk drive mainly reads the required data from the optical disk, so the reading efficiency of the optical disk drive cannot be effectively enhanced when the data is read by way of track jumping in the optical disk drive. Therefore, the conventional method for the optical disk drive for reading the data on the optical disk still has problems to be solved.